The primary objective of this project is the elucidation of the mechanism, structural foundation and regulation of basic biological processes involving movement at the subcellular level. Our analyses include: chromosome movement, mitotic spindle assembly and movement, cell division and other labile motile events which share in common the attribute of transient assembly and organization of microtubules and microfilaments. We approach this objective by developing and applying new optical mechanical, photochemical, thermal, electro-optical, electro-mechanical and other methods which allow measurement of physical parameters directly in localized regions in functioning living cells. High resolution polarization microscopy is used for detecting and measuring birefringence; microtensiometry and micromanipulation are used for analyses of mechanical properties; and microinjection and microbeam irradiation are used for local modulation of organellar environment. Immuno-fluorescence and electron microscopy complement the in vivo studies. Thermodynamic analyses and model building as well as studies of the basic physical principles underlying the measurements are an integral part of the effort.